Optical viewing system for work chambers

ABSTRACT

An optical system for illuminating, viewing and aligning work in a vacuum chamber. The apparatus is predicated on the use of a clear or reflectively coated glass strip which becomes and remains a mirror surface as vapor from the material being worked is deposited on the glass surface. The duration of the permitted exposure is a function of the material type and the quantity of vapor released. The glass strip is then indexed to expose a new clear surface.

1 Mai -12:1, 51a

l 1 119104 GR 307020388 1 States Patent [151 3,702,388

[451 Nov. 7, 1972 [54] UP'MMIAL VIEWING SYSTEM FOR 3,169,183 2/1965Radtke et al ..2l9/12l EB WURK CHAMBERS 3,465,119 9/1969 Larson..219/l21 EB [72] inventor: James King, Tustin Cant 3,497,665 2/1970Gerard ..219/12l EB [73] Assignee: Union Carbide Corporation, NewPrimary E xaminerJ. V. Truhe York, NY. Assistant Examiner-Gale R.Peterson [22] Filed: Nov. 9, 1970 Attorney-Paul A. Rose, Harrie M.Humphreys and Dominic J. Terminello [21] Appl. No: 87,854

[57] ABSTRACT 52 11s. o1. ..219/121 EB An optical system forilluminating. v g and alig- 51 1111.1c1. ..B23k 15/00 e k in a vacuumchamben The apparatus is [5 11 m 1f Search 9 R 121 L 121 B predicated onthe use of a clear or reflectively coated 118/7 350/19 glass strip whichbecomes and remains a mirror surface as vapor from the material beingworked is [56] References Cited deposited on the glass surface. Theduration of the permitted exposure is a function of the material typeUNITED STATES PATENTS and the quantity of vapor released. The glassstrip is 2,910,913 11/1959 Michel ..350/19 mdexed expse a new clearSurface 3,156,810 11/1964 Samuelson ..219/l21 EB 8 Claims, 4 DrawingFigures WINDOW 0x PATH FOLDlNG M RRORS 26 BINOCULAR \TELESCOPE I fQ Q$'E: J U

IMAGE AFTER RETICLE CROSSHAIR 22 RETICLE IMAGE AFTER OBJECTIVE LENSPKTENTED 7W? 3,702,388

wmoow c PATH FOLDING 26 BNOCULAR MIRRORS \TELESCOPE //2 *BE L ewaa 0FIG- /8 CROSSHAIR RETICLE F/ G. 3. IMAGE AFTER 45 32 4/ OBJECTIVE LENS I44 40 LIGHT PATHfi VAPOR Q42. MIRROR ANGLE MIRROR ANGLE L *2 MAGNIFIEDIMAGE AT EY EPlECE \NVENTOR A ORNEY GlPTlltCAf WEWING SYSTEM FOR WORK@TTAMBERS This invention relates to an optical system for viewing aworkpiece to be worked with a beam of energy, and more particularly tosuch a system for viewing a workpiece from outside a vacuum chamber inelectron beam working of materials.

While the invention may be used with any beam source of energy whereinmetallic vapors are given off by the workpiece, it is ideally suited forelectron beam welding, cutting and machining, etc. of a metallicworkpiece and for purposes of simplifying the description, referencewill be made hereinafter to electron beams primarily.

Electron beam working is carried out in a sealed chamber under highvacuum. Thus, once the chamber is closed and the operation begun, theremust be provided some system for viewing the workpiece. Generally, suchsystems must also provide a means for accurately aligning the joint tobe worked with the electron beam. lf the joint is not aligned with oneof the axes of motion with the chamber open, it can never easily berealigned when the chamber is evacuated,

and, therefore, out of the operators reach.

The prior art contains several optical systems for aligning and viewinga workpiece. However, all of the prior art systems have one outstandingdrawback. In every case, the prior art utilizes a highly polishedmetallic mirror surface to reflect the image of the workpiece back to atelescope outside the chamber. Also, in every case great care andelaborate systems have been designed to keep such highly polishedmetallic mirrors from receiving or coming in contact with the metallicvapors being generated by the workpiece being treated. Several prior artsystems provide an apertured, highly polished mirror, mounted atapproximately 45 to the electron beam, inside the electron beam gunitself, or a protective housing including a protective shutter toprevent vapor from reaching the mirror.

All of these procedures, obviously, add cost and/or complicatedmechanisms to the electron beam machine.

The same metal vapors from the working operation .that affect theoptical system also act to cover any exposed surfaces and eventuallycause all transparent members to become first translucent and finallyopaque. f the two types of illuminating systems now in use for opticalsystems, one projects the illumination through the same lenses used forthe optical viewing path, and the other makes use of a light sourceprojected directly at the surface of the work.

Since the vapors from the workpiece travel in line of sight paths, theexposed lens or bulbs of the light source pointed directly at the workare quickly plated with the vapors, and the light is diminished as thelens becomes translucent and almost completely blotted out as thecoating density increases. Since the coating is reflective on the sideof the lens or bulb facing the light source, the light is reflected backtoward the source rather than transmitted toward the work. The samephenomena occurs when the light is directed through a viewing lens andthe cover glass. Although the vapor improves the reflectivity of asurface, the same amount of vapor decreases the transmission of thelight drastically. Since the viewing path depends upon the reflectedlight traveling back from the surface through the lenses to reach theviewers eye, the brightness of the image being viewed depends upon theillumination initially placed on the surface. Any vapors on the coverglass or on the lenses that reduce the transmission of the illuminatinglight also necessarily reduce the light reflected back along the samepath for viewing. An optical viewing system of the type universally usedfor the electron beam welding process is best described as an opaqueprojector. This means that when an opaque, but at least partiallyreflecting surface, is illuminated by a light source, a certain amountof the light will be scattered; however, a small percentage of the lightwill be reflected into the optical viewing system. The brightness of theimage being viewed, therefore, is always much less than the brightnessof illumination. The rather faint reflection from the surface mayfurther be reduced by other losses that occur in the optical column suchas reflection from lens surfaces or transmission reduction due to vaporcoating of cover glass or lens surfaces in the optical path.

Accordingly, it is the main object of this invention to provide asimple, low cost, optical viewing and illuminating system for electronbeam machines producing an image of maximum brightness for a substantialperiod of time.

A second object is to provide an optical system wherein the reflectingmirror is placed in the vicinity of the workpiece and is coated with themetallic vapors given off by the workpiece.

It is another object to provide an optical system which is unrestrictedby apertures in the gun.

Yet another object is to provide a system of illumination separate fromthe optical viewing column, so that internal lens flare is avoided, butarranged in a manner so that the light intensity is maintained at anadequate level regardless of vapor deposition.

These and other objects will either be pointed out or become apparentfrom the following description and drawings wherein FIG. 1 is aschematic drawing of the various pieces of apparatus embodying one formof the optical system of the invention;

FIG. 2 is a schematic drawing of the optical system showing illuminationsources mounted on the system;

FIG. 3 is a side schematic of the arrangement of the illumination systemand its self-perpetuating mirror;

FIG. 4 is a side schematic view of the optical system showing theoptical finder element.

As briefly mentioned above, all presently known viewing systems haveutilized a mirror placed at approximately a 45 angle to the center lineof the electron beam gun and mounted up inside the gun. The mirrorreflects the surface of the workpiece along a line of sight to amagnifying eyepiece which is outside the chamber. These systems onlypermit viewing while welding for very few seconds, depending upon theamount of vapor generated by the process. The 45 mirror is usuallyprotected from the metal vapors and other contaminants arising from thesurface of the work during welding, by means of a cover glass which isplaced some distance below the mirror, normal to the line of sight. Asthe evolution of metal vapors from the weld coats the surface of thecover glass very rapidly, the percentage of transmitted light is rapidlyreduced. After the cover glass becomes opaque, it may be indexed throughsmall increments to expose a new, clear surface of the glass. These newsurfaces, in turn may last only a few seconds as well.

The same metal vapors from the working operation that affect the opticalsystem also act to cover any exposed surfaces and eventually cause alltransparent members to become first translucent and finally opaque. Ofthe two types of illuminating systems now in use for optical systems,one projects the illumination through the same lenses used for theoptical viewing path, and the other makes use of a light sourceprojected directly at the surface of the work.

The present invention provides an optical system which, for the firsttime, places the mirror system below the gun rather than up inside thegun and overcomes the above limitations by utilizing a 6-inch strip ofcoated or clear thin, flat glass or metal as the mirror, without anyprotective covering. It should be noted that the same system couldoperate from a position within the gun structure, but it is lessdesireable in such a position. The glass, or metal, is coated by themetallic vapor as the welding action begins and is maintained as a veryadequate front surface mirror. The same thickness of vapor coating thatwould render a cover glass opaque to transmitted light, in the prior artsystems, actually improves the reflection of light from the reasonablyoptically plane surface of the glass slide. The reflection capabilitiesof this mirror may last for a period of several minutes or even hourswhile welding aluminum, and somewhat less time when welding titanium,steel, and other materials. If the mirror surface becomes degraded, itis mechanically moved laterally a fraction of an inch to expose a cleansurface, which then becomes coated and acts as a new mirror. As there isno cover glass to become occluded, the life of the mirror is onlylimited by the excessive build-up of vapors which, in the case of steeland similar materials result in a flaking action after about tens ofseconds of operation. Thereafter, the glass, or metal, must be indexedto present a clear surface. The duration of the permitted exposure is afunction of the material type and the quantity of vapor released fromthe melt.

Referring now to the drawings, in FIG. 1 the mirror assembly 10 ismounted on the lower end and depends from the electron beam gun 12. Themirror assembly 10 is pivotally mounted so that the angle may be variedfrom about 40 to about 50 for reasons to be explained hereinafter. Theremainder of the optical system includes an objective lens 14 having amanual or motorized adjustment 16 to adjust its position to focus thevirtual image of the mirror on the plane of the crosshair reticle 18.The reticle 18 may be either fixed, or moveable. A collimator lens 20 ismounted to view the crosshairs and produce a collimated beam of light ofparallel rays having no distince focal point. Due to the absence of afocal point, the projected image can be viewed at any point along itspath as a clear, complete image. These elements may be in a straightline or as shown in FIG. 1, mirrors 22 and 24 may be used to fold thepath of light rays to conserve space.

Outside the work chamber C, or inside if required, and in line with theparallel rays of the collimator lens 20, is mounted a monocular orbinocular magnifier 26, usually in the form of a telescope, which viewsthe image projected by the internal optics through a win- 26 is alsoseen through an optical finder 28 mounted in the optical column of theoptical system. The optical finder 28 consists of a right angle prism(or mirror) and a magnifying eyepiece. The assembly is mounted in a tubewith an eyepiece at one end and prism at the other. The prism isinserted into the optical column above the crosshair reticle so that theoptical finder views the image of the work surface which has beenprojected onto theplane of the crosshairs by the objective lens in thesame manner as described for the opera tion of the collimatingsystem.'The viewer may then adjust the focus of the objective, selectthe desired field of view, and align the crosshair to the target. Inoperation, when the chamber C is opened, the operator may view theworkpiece image 30 through optical finder 28 while he adjusts theworkpiece location, because he now is in easy reaching distance of thework in the chamber. The optical finder allows a single operator toinitially set up the system by aligning the crosshair image to the work,focusing the objective lens, selecting the field of view and adjustmentof the illumination level and image.

Referring to FIG. 2, a lighting system provides two light sources 32,one on each side, to provide shadow control and illumination of thesurface to be viewed. The light beams from two focusable projector typelights are directed into the self-coating mirror 10 mounted at anappropriate angle. The light sources themselves are mounted so that theymay be adjusted angularly or linearly so that the reflected light may beproperly directed on the work surface. The lights may also be projectedon the work surface as described in FIG. 3.

FIG. 3 schematically shows the relationship between the light source andan associated self-perpetuating mirror.

In use, clear cover glass 41 covers mirror 40. Initially, the lightoriginating at the bulb 44 goes through lens 45 and the cover glass 41and is reflected from the original light path toward the work surface.The mirror mount 43 is free to rotate relative to the housing so thatthe light output may be directed to any desired point on the worksurface. As the work progresses, vapors plate the surface of the coverglass 41 protecting the mirror 40 forming a reflective surface, thereby,continuing the reflecting function of the mirror assembly. Since thissurface is used for light reflection only rather than critical precisionviewing, the coating may be allowed to accumulate without indexing andwithout inhibiting its function.

On the other hand, if the bulb 44 and lens 45 assembly were pointedtoward the vapor source, they would become occluded by vapor plating inan extremely short time.

According to the concept of the invention, the mirror 10 is eitherdirectly in the line of sight of the operator or is in the optical lineof sight after collimating lens 20, mirror 24, reticle 28, mirror 22,and objective lens 14. If the operator were using the naked eye toobserve the reflected image of the work surface, the image would alwaysbe seen in focus. This is because the human eye automatically refocusescontinuously to follow a moving object (a process known asaccomodation).

When magnification of the image is required, which is usually the case,a magnifier in the form of a telescope is used by the operator to viewthe image in the mirror. A telescope has a definite focal length andmust be adjusted to focus either near or far objects. Therefore, eventhough the telescope provides magnification, it defeats the ability ifthe eye to maintain continuous focus. The depth of focus of most opticalinstruments increases with increasing distance and decreases withdecreasing distance. Therefore, the adjustment of focus at relativelyclose distances becomes critical.

The viewing distances are small in moderate electron beam work chambersizes (6 inches to 60 inches as an example). in the case of a mirroroptical system used with a moving gun, the mirror to telescope distance(X distance) may change continuously while welding with the gun. Asamatter of less importance, the mirror to work distance (Z distance) mayalso be changed occa sionally to accomodate changes in working distanceof the electron beam gun.

in order for the optical system to automatically function in the samemanner as the naked eye (accomodation), it is desirable that the systemcontinuously maintain focus over the entire X axis movement for a givenZ axis distance.

lln the embodiment shown in FIG. 1, the telescope 26 is focused atinfinity so that the output of the collimating lens M will always remainin focus even though the mirror lit) to telescope distance X is changed.

The mirror to work surface distance Z may be optically focused manuallyby the objective lens 14. The objective lens M is designed to focus overthe usual welding range of 3 to 18 inches which means that the worksurface may be manually brought into sharp focus within that range,although greater and lesser distances could be used. The objective lensis mounted so that it can be moved forward or backward in the opticaltube.

The position of the objective lens 14 is regulated according to thedistance of the object, so that the image falls on the plane of thecrosshairs 18. Thus, the crosshairs and the image combine on thecross-hair plane (see 4%, FllG. i) so that the crosshairs appear at acertain point on the virtual image in the mirror. Therefore, they appearto the observer at a certain point on the object.

Because the mirror, the objective lens, and the crosshair reticle movetogether as a unit on the electron beam gun, the location of thecrosshair, once set, may be made to unvaryingly represent the axis ofthe electron beam gun for a given gun to work distance.

The mirror assembly is made variable to satisfy two purposes: A fixedmirror angle cannot cover the required field of view at the work surfaceover the designed variation of mirror to work distance. The expectedrange of adjustment of the mirror to cover the work surface at alldistances is from about 20 to 70. If this angle is made continuouslyvariable, the apparent crosshair position relative to the image may beminutely adjusted to bring it to the center of the viewing field tocoincide with the axis of the electron beam gun, or to view some offcenter point, a combination of linear and angular motion can be used toachieve this adjustment.

As will be noted from the above, the subject invention allows one manalone to view the crosshair position at the same time that he is inposition to conveniently manipulate the piecepart location by making useof the optical finder eyepiece which is mounted in the optical systemcarried inside the chamber.

Having described the invention with reference to certain preferredapparatus and arrangements thereof, it should be understood that certainmodifications may be made to such apparatus or the arrangements thereofwithout departing from the spirit and scope of the invention.

What is claimed is:

1. In metal working apparatus, employing an energy beam generating gun,including an electromagnetic lens for working metals which give offmetallic vapors, the combination with a vacuum work chamber within whichsaid gun is mounted for adjustable movement in vertical and horizontaldirections and worktable means located in said vacuum work chamber forsupporting metallic workpieces for movement horizontally in the X and Ydirections; of an optical system for viewing the workpiece including anunprotected mirror assembly mounted on, and depending from the lower endof said beam generating gun, and including a mirror for reflecting lightrays from the surface of the metal to be worked; said mirror beingcoated by said metallic vapor from said metallic workpiece as the beamworking operating proceeds to temporarily maintain an adequate mirrorsurface; indexing means in said mirror assembly for exposing a newmirror surface when the exposed surface becomes degraded; and atelescope located outside of said chamber and being so positioned as toview the image reflected by said mirror.

2. Apparatus according to claim 1 wherein said mirror assembly ispivotally mounted on said gun.

3. Apparatus according to claim 1 including an objective lens; acrosshair reticle located in the path of the image forming rays passedby the objective lens whereby said image and crosshairs aresuperimposed; and a collimating lens which collimates and directs therays of the image and crosshairs to said telescope.

4. Apparatus according to claim 3 having an optical finder locatedbetween said objective lens and said collimating lens to view saidsuperimposed crosshair and image such that an operator may makeadjustments to said objective lens while viewing said superimposedimages through said optical finder.

5. Apparatus according to claim 3 wherein illumination sources aremounted adjacent said objective lens so that the rays of light areprojected into said mirror assembly for reflection to the workpiece.

6. Apparatus according to claim 3 including an illumination sourcecomprising a housing, a bulb mounted in said housing and a mirrorlocated in said housing and at an angle to the optical axis of said bulbfor reflecting light from said bulb through an aperture in said housing,said mirror being free to rotate relative to said housing to direct thereflected light at any desired spot.

7. Apparatus according to claim ll including a reflecting system betweensaid mirror assembly and said telescope, comprising an objective lens; afirst reflective surface to reflect the image forming rays passed by theobjective lens at about 45; a crosshair reticle located in the path ofsaid reflected image forming rays whereby said image and crosshairs aresuperimposed, a second reflective surface which reflects the image andcrosshairs at about 45, and a collimating lens which collimates anddirects the rays of the reflected image and crosshairs to saidtelescope.

8. In metal working apparatus, employing an energy beam generating gun,including an electromagnetic lens for working metals which give offmetallic vapors, the combination with a vacuum work chamber within whichsaid gun is mounted for adjustable movement in vertical and horizontaldirections, and worktable means located in said vacuum work chamber forsupporting metallic workpieces for horizontal movement thereof; of anoptical system for viewing said workpiece comprising being positioned toview the image reflected by said mirror surface.

1. In metal working apparatus, employing an energy beam generating gun,including an electromagnetic lens for working metals which give offmetallic vapors, the combination with a vacuum work chamber within whichsaid gun is mounted for adjustable movement in vertical and horizontaldirections and worktable means located in said vacuum work chamber forsupporting metallic workpieces for movement horizontally in the X and Ydirections; of an optical system for viewing the workpiece including anunprotected mirror assembly mounted on, and depending from the lower endof said beam generating gun, and including a mirror for reflecting lightrays from the surface of the metal to be worked; said mirror beingcoated by said metallic vapor from said metallic workpiece as the beamworking operating proceeds to temporarily maintain an adequate mirrorsurface; indexing means in said mirror assembly for exposing a newmirror surface when the exposed surface becomes degraded; and atelescope located outside of said chamber and being so positioned as toview the image reflected by said mirror.
 2. Apparatus according to claim1 wherein said mirror assembly is pivotally mounted on said gun. 3.Apparatus according to claim 1 including an objective lens; a crosshairreticle located in the path of the image forming rays passed by theobjective lens whereby said image and crosshairs are superimposed; and acollimating lens Which collimates and directs the rays of the image andcrosshairs to said telescope.
 4. Apparatus according to claim 3 havingan optical finder located between said objective lens and saidcollimating lens to view said superimposed crosshair and image such thatan operator may make adjustments to said objective lens while viewingsaid superimposed images through said optical finder.
 5. Apparatusaccording to claim 3 wherein illumination sources are mounted adjacentsaid objective lens so that the rays of light are projected into saidmirror assembly for reflection to the workpiece.
 6. Apparatus accordingto claim 3 including an illumination source comprising a housing, a bulbmounted in said housing and a mirror located in said housing and at anangle to the optical axis of said bulb for reflecting light from saidbulb through an aperture in said housing, said mirror being free torotate relative to said housing to direct the reflected light at anydesired spot.
 7. Apparatus according to claim 1 including a reflectingsystem between said mirror assembly and said telescope, comprising anobjective lens; a first reflective surface to reflect the image formingrays passed by the objective lens at about 45*; a crosshair reticlelocated in the path of said reflected image forming rays whereby saidimage and crosshairs are superimposed, a second reflective surface whichreflects the image and crosshairs at about 45*, and a collimating lenswhich collimates and directs the rays of the reflected image andcrosshairs to said telescope.
 8. In metal working apparatus, employingan energy beam generating gun, including an electromagnetic lens forworking metals which give off metallic vapors, the combination with avacuum work chamber within which said gun is mounted for adjustablemovement in vertical and horizontal directions, and worktable meanslocated in said vacuum work chamber for supporting metallic workpiecesfor horizontal movement thereof; of an optical system for viewing saidworkpiece comprising an unprotected mirror assembly mounted on, anddepending from the lower end of said beam generating gun, and includinga clear glass slide which is transformed into a mirror surface asmetallic vapors are collected on said glass slide for reflecting lightfrom the surface of the metal to be worked; indexing means in saidmirror assembly for exposing a new surface of said glass slide when theexposed surface becomes degraded; and a telescope located outside saidchamber and being positioned to view the image reflected by said mirrorsurface.